Optimisation of fermentation conditions of exopolysaccharides produced by "Hua 5" and their bioactivities

Abstract

In this study, "Hua 5" strain collected, isolated and purified in the field was selected as the research object. The strain was identified by traditional morphology and molecular biology. The fermentation conditions of exopolysaccharides produced by "Hua 5" strain were optimized by single factor and response surface tests. The structural characteristics of exopolysaccharides were detected by Fourier infrared spectroscopy, and the in vitro immune activity and anti-tumor activity of exopolysaccharides were detected by cell viability assay kits. The results showed that the strain was identified as Lepista sordida, and the optimal fermentation conditions for the production of exopolysaccharides were temperature 25 ℃, inoculum 90 mg/100 ml, and rotation speed 180 r/min. Under these conditions, the exopolysaccharides contents could reach 6.01 g/L. The infrared spectrum results showed that L. sordida exopolysaccharides had the pyranose structure. The biological activity tests results showed that L. sordida exopolysaccharides could significantly promote the proliferation of mouse macrophages RAW 264.7 (P<0.05), and the proliferation rate showed a dose-dependent increase. When the mass concentration of L. sordida exopolysaccharides was 20 μg/ml, the proliferation rate reached 50.16%. The L. sordida exopolysaccharides could significantly inhibit the proliferation of mouse gastric cancer cells (MFC) (P<0.01). When the mass concentration of exopolysaccharides was 5 μg/ml, the inhibition rate reached 53.41%. This study preliminarily verified that L. sordida exopolysaccharides had certain immunomodulatory and tumor inhibition effects.

Keywords

• lepista sordida|exopolysaccharide|fermentation condition optimization|response surface analysis|bioactivity